1. Field of the Invention
The present invention generally relates to a curable sealer and/or adhesive composition having improved adhesion to paints. The invention also relates to a method, and the coated substrates formed by the method, where a paint is coated over such a curable sealer/adhesive composition in a dry state to provide a paint, upon drying, having improved paint adhesion.
2. Description of the Related Art
It has been observed that certain conventional seam sealers based on polyethers having hydrolyzable silicon-containing end groups have exhibited poor adhesion to some automotive aftermarket paints when the paint is applied onto the sealers in instances where the sealers are previously allowed to cure dry for more than 12 hours before application of the paint thereon. Examples of such conventional seam sealers are described, for example, in U.S. Pat. No. 3,971,751 to Isayama et at. and U.S. Pat. No. 4,444,974 to Takase et at. It is often the case that a seam sealer will be applied onto the exterior a vehicle being repaired where the seam sealer, as applied on the vehicle, is left to cure for a relatively extended period of time, for example, while other projects demand a user's attention, or overnight or over a weekend before the user has an opportunity to apply the paint over the seam sealer. Since such unplanned or unavoidable extended delays can and do arise, in practice, before a paint can be applied to a previously applied sealer, it has been observed that the conventional silane-capped sealers have suffered in these circumstances from the drawback of exhibiting extremely poor paint adhesion and even adhesive failures. To address this problem, user was effectively required to plan and commit to completing both of the separate procedures of applying the seam sealer and thereafter applying the paint onto the seam sealer within a relatively short time frame to ensure adequate adhesion was formed betwen the seam sealer and the paint. Because of the often competing demands for the time of a user, this inconvenience and loss of flexibility in the timing for applying the different coatings is highly undesirable.
As can be understood from the above, the formulations of conventional seam sealers based on polyethers having silicon-containing hydrolyzable end groups which have been proposed to date, have disadvantages and as yet unsolved problems if allowed to cure for more than about 12 hours after application and then are used in conjunction with automotive paints.
U.S. Pat. No. 5,272,224 to Baghdachi et al. describe a one-component, moisture-curable polyurethane-based adhesive composition comprising a silane-terminated polyurethane of a prescribed formula, where the composition is useful for affixing glass panels directly to electrocoat painted metal substrates or over a primer comprising a polyurethane base polymer containing an electrocoat adhesion promoter. As one of the optional adjuvants for the composition described by Baghdachi et al., there is a fiexibilizing agent added to the composition in amounts of from about 1.0 to about 10.0 parts by weight fiexibilizing agent, preferably from about 2.0 to about 5.0 parts by weight, based on 100 parts by weight of the polyurethane base polymer. As suitable fiexibilizing agents, Baghdachi et al. mention dioctyl phthalate, dibutyl phthalate, diundecyl phthalate, dioctyl adipate, butyl benzyl phthalate, iodecyldiphenyl phosphate, N-butyl-p-toluenesulfonamide, and N-ethyl-p-toluene-sulfonamide.